Just to make one thing clear after Wouters inflammatory soap box speak. The F16 rules dont allow any meaningful use of banana boards. Boards can not deviate more than 6 degrees from the vertical. But this discussion is about the A class.




I agree with Jake, and I think most others do.
I have no doubt that the A-class will manage this well, just like they have in the past with the Wing and other things.

We have heard many claims of that extent in the last year alone. The LR2 A-cat was going to roll the A-cat Worlds, otherwise the solid Hall spars wing would. The C-class competition was going to be dominated by the full foiling entry. The Moth foilers were going to destroy the moth class once and for all !

Yet in all these instances, the outcomes were directly opposite.

I mean did the introduction of the carbon mast kill the A-cat class in the early 90's ?

Why are we all so scared of NOTHING !

You will all find out once more that I'm right were you all are wrong.

Halve of you don't even really understand what you are talking about.

The other halve is to dumb or lazy to look up past experiences with similar projects and make a balanced judgement. Lots of things have been tried before and by far most of them have been found wanting. It is only the predictable hysteria about "obsoleteness" that gives many of these projects alot more weight then they deserve. Give them a few more months and 90% of them will quietly disappear into the background, never to be heard off again.

When ohh when do we smarten up ?

Wouter

For the technical engineerting types out there, I have a question about these bannana boards. Seems to me the only reason we use daggerboards at all is to prevent sideslip, am I correct?

And for the past many years, the development of boards has been aimed at making the boards more efficient, in the way of lift vs. drag, is that correct? (please stop me when I get off track) and we are trying to get the boards to be as "high aspect" as possible, like the wing of a glider, to both prevent sideslip and also create lift to the windward mark, ie. upwind lift, (not lifing the boat out of the water), but keeping the boat from sliding downwind, as in better VMG to the windward mark, correct?

Now we see these curved boards, which seem to me to be a small step backwards in the whole development of higher aspect, better vmg type boards. Seems to me, with the board curved up under the hull, you are losing some amount of side-slip reduction, in the way of vmg to windward. As I understand these boards, their purpose is to lift the low hull up out of the water a little bit, never clear of the water, but up a little bit. But what about sideslip?

We see these boards on the ORMA tri's but they have a deep daggerboard in the center hull for vmg type lift, their bannana boards on the Ama's are to help keep from stuffing the ama's, or so I thought. They are not there to generate lift to windward, that is the job of the much larger, deeper, center hull daggerboard, or am I wrong here?

I don't see how bannana boards on a cat, with no other daggerboard to help generate vmg to windward type lift, will help you get to the A mark faster.

But I'm not an engineer, just a pilot who has never seen -curved- upward (or downward) wings. <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

Tim,

what about the 777? That wingspan flexes upward a good bit when flying (something like 15 feet?). I'm sure they planned that (probably for stability), but it does look weird...

I'm sure it's not the same thing....

Tim,

Finally, somebody who is using his brain !

The only cat that has been succesful in fleet racing has exactly that setup Tim. A seperate set of daggerboards and angled (bruce) foils.

This is John the Vries White formula 20.

Interesting to note that the F16 class rules state that only a pair of daggerboards may be used, not a quad ! Prophetic vision, maybe. Or just a cold hard analysis and judgement that was had 6 years ago, by someone who tried hard to seperate the emotional from the hard technical facts ?

Time and you all be the judges of that !

Wouter

The boat with the boards in front is not build or designed by Nils but designed by Martin Fisher and i do not know who build it.
The banana boards is also not new in A-class because PJ of the Dutch A-class did used the banana boards already 2 years ago and he found out that there was not a real advanced better performance of the boat with the boards.

I also think that every body was getting nervous because the guy who was in front a couple of times ( Bob Baier ) using the
banana boards and they had the idea that this was the big trick but they forgot that he trained the last couple of months 4 days a week , so he is really a trained sailor and a good sailor and when the wind conditions where changing he did not win the races anymore, so are the boards really the trick. I don't think so and to be honest on what i have seen it is NOT the trick.

The class rules on boards is also set and it is not allowed to have the tips of the banana boards closer together then with a gap of 1,5 meter when they are full down and they have to stay within the boat width when they are in the hulls at the bottom so this makes it already more limited.

I think everybody is seeing a bigger ghost then there really is.

Cheers,

Hans Klok

Jay, you are right, it's not the same thing.

The wing flex of a big airline type plane is engineered in for several reasons,

1. The plane would be too heavy to build a solid wing with no flex.

2. The ride for the passengers would be extremely rough in any kind of turbulence if the wings didn't flex at all (the are like shock absorbers)

3. Using today's building materials (aluminum) it is most "cost effective" to build -for- the flex instead of trying to build -out- the flex.

But, the new 787's are being designed and built of Carbon Fiber, to save weight. I'm not fully aware of what they are doing with the wing on that, but less flex at takeoff would give it more lift, ie. higher payload, which is what it's all about in comercial aviation.

Wings do flex quite a bit at takeoff, ever seen a fully loaded 747 take off? WOW, those wings really flex up!!

But some amount of lift is lost as they bend up, no doubt. Once the plane levels off at cruising altitude, the wings are not so bent, only when you hit turbulence will you see the wingtips flapping up and down! Quite funny to see really, but necessary to give a smoother ride.

I know there are some guys on this board who actually work for Boeing so maybe they can help me out here with a fuller explanation on how they engineer them.

Why are you so angry?

I believe Ben Hall made it quite clear that he didn't know what the wing sail was going to do and nobody in the class jumped and banned it. I don't recall anyone (with any real information) claiming it was going to kill the class. Same thing with the foiling C-class...it certainly had a buzz around it but everyone knew that it was new and there were going to be teething problems. This is the normal progression of things.

I look at instances like this and really feel good about the way the class is running things. They don't jump to conclusions; they didn't shout and have a knee-jerk reaction to Ben's wing...they let it play out. They're very likely going to do the same thing here...let the bannana foil either prove itself or not. The class will decide something only when there is enough information to decide something. Beyond that, this is all conjecture and fun to consider.

I do firmly believe that a rigid wing could be made to be faster than fabric sails and that a foiling C-class will eventually perform better. All of this is only a matter of the time and effort required to hammer out the details and do the development. Currently, the challenges seem to be slightly beyond the motivation of these development minded individuals. But motivations will change, things will progress, and we will move forward.

I think you are right Jake. I watched the Moth Foiler develop. At first look, I thought, no way, it'll be too hard to sail...now everybody's doing it.

I think we may see that next in cat speed development, if we allow it. I think it could eventually be done cheaper and easier than bannana boards, or the wing sail, but I like the idea of both, when it comes down to a total package for the future.

But for now, if we could just get the price of carbon fiber down to equal regular fiberglass... <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

No? Well if you accept a tail as a sort of wing, have a look at the attached picture.

If you want to create lift and sideforce, canted or bended wings are a good solution. You can use two boards, one for each job. But with a single bended or canted you save a lot of wetted area, which is drag. As long as the board can carry the loads, it is a good solution.

Cheers,

Klaus

... and a second picture. Showing wing tips, again not pure 0° and 90° but something in between.

On spot, but the quoted sentence may be misunderstood. The boards are not supposed to create unlimited "lift to the upwind mark", only the necessary to keep forces in balance. The boat automatically adjusts the leeway angle (angle of attack) so the underwater lateral lift component is kept equal to the aerodynamic lateral lift component (sails).

I would also like to add some important details, however obvious for some of you:

1) Some designers prefer to separate vertical and horizontal foils in order to optimize each specialized foil independently (example: Rave and Trifoiler).

-Vertical boards are optimized to generate lift with minimum angle of attack and drag.
- Horizontal boards are optimized to generate a definite lift to keep the boat at the desired attitude (lift = part of the boat weight) or foilborne (lift = total boat weight)with minimum drag, regardles the angle of attack.

2) Other designers prefer canted boards/Bruce foils because they make it easier to self-stabilize the boat. Their lift is in the general direction of the sails' center of lift, so the boat almost wouldn't heel when foilborne. Take a look at Hydroptére.

3) If we disregard weight, complexity, price and other practical aspects, the best performance should be with a pair of vertical asymetric foils for lateral lift, plus a pair of canted/banana foils or horizontal foils (not sure which one) for horizontal lift.

4) It is not for performance reasons that ORMA 60 tris use curved/banana boards instead of straight boards: it is for practical reasons. My 27 ft tri has straight canted boards and the most difficult task on board is to insert and remove them from the amas. I can't imagine doing that on a singlehanded 60ft tri.

- It is a lot easier to handle a large curved board than a large straight board. Ian Farrier was probably the first to notice this and designed the F27 prototype with curved foils. The straight foils hit the dock when up, so you can't dock unless you take them out or live them in the water.
-The advantage of canted/banana boards vis-a-vis horizontal foils is the ability to reduce their span (raise partially or totally).
- It is a lot easier to raise a curved board than a canted straight board. A curved foil can be "hoisted" from the shroud or mast, but how do you pull a long and heavy straight board to the outside of a float?



Photo taken after the first sea trial: the board doubles as a backrest for the crew after the first attempts to pull it out failed. The applause is sarcastic.

Regards,

and finally
[img] ]http://www.a-richter.de/bilder/foto/moewe.jpg[/image]

I would appreciate if somebody could tell me how to embed pictures directly in the postings.

Cheers,

Klaus

Somebody mention wings curved upwards?

Hobie Hawk, circa 1973:

Yes, it's on the winch, but the wings curve upwards without the loading.

NASA's Helios, electrically powered flying wing.

Geeesh....What DIDN'T Hobie build at one time or another?

At the risk of going farther off topic:

Aren't winglets at the end of wings more for stability, and to reduce wingtip vortices that can partially stall the wing? It can't directly be a lift thing.

I have always been told the upturned wingtips, blended or otherwise, were to reduce the tip votex's and thereby reduce drag, not to increase lift.

And on the gliders, again, it would be too heavy to build a stiff wing that didn't bend at all. If you build it light, it will bend. I don't see how the bent up wings can increase lift in the vertical, as lift acts perpendicular to the lifting surface, correct?

You realize that the tail of a conventional airplane like the picture of the V tailed Doctor Killer actually "lifts" in the downward direction, to point the nose up and balance the airplane about the center of lift, which is somewhere in the main wing. It is actually acting against total uplift. It is exactly like our rudders on cats, you push on the tiller, make the stern of the boat go down (or away from the direction you want to go), so the bow will go up, like a teeter-totter, it pivots about the daggerboards (wings).

That is why Rutan designed canard type airplanes, (they tried this on an earlier America's Cup boat back in the 80's too, putting the rudder in the front to increase lift when turning) where the canard is in the front of the main wing, and does help to lift the total weight of the airframe along with the main wing. And he designed it so the canard would stall before the main wing stalled, so it was much safer. I don't know why Boeing never built one too.

Here's some light reading on the subject of Burt Rutan's designs. Now, if we could just get him to design catamarans... <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />

http://www.rutanaircraft.com/htmlpages/airplanes.html

The following quote from See How It Flies, 3.12.1 affirms that the winglets are used to increase lift:



Edited to display the key statement in bold.